<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        /* ul li{border: red 1px solid;} */
        #list>li{border: red 1px solid;}

        div{width: 300px;height: 300px;background: red;}
        div:hover{background: blue;}
        div:active{background: green;}

        a:link{color: red;}
        a:visited{color:blue;}
        a:hover{color: green;}
        a:active{color: yellow;}


        div:after{content: "world";color: yellow;}

        :checked{width: 100px;height: 100px;}
        :disabled{width: 100px;height: 100px;}
        :focus{background: red;}

        li:nth-of-type(2){background: yellow;}
    </style>
</head>
<body>
    <ul id="list">
        <li>
            <ul>
                <li></li>
                <li></li>
                <li></li>
            </ul>
        </li>
        <li></li>
        <li></li>
    </ul>
    <ol>
        <li></li>
        <li></li>
        <li></li>
    </ol>

    <div>hello </div>
    <a href="#">这是一个链接</a>


    <input type="checkbox">
    <input type="checkbox" checked>
    <input type="checkbox" disabled>

    <input type="text">

</body>
</html>